The US is sending more combat assets - including F-35 stealth fighter jets - to the western Pacific as the North Korea nuclear crisis escalates.

A second aircraft carrier has arrived in the region in Washington's latest show of force following a series of missile and nuclear tests by Pyongyang.

The USS Theodore Roosevelt strike group entered the western Pacific on Tuesday and will soon join the USS Ronald Reagan off the Korean peninsula, just weeks before US President Donald Trump travels to the area.

In just a few weeks the US will move 12 F-35A Lightning II stealth fighter jets to Japan for the first time, along with 300 airmen, for six months.

The announcement came on the same day a North Korean diplomat urged the US to make the "right choice" and recognise it as a nuclear-armed state as a "way out" of the current showdown.